There are others, of course. Some we know of, and likely many others that have yet to be identified.

Two relatively obscure viruses - Inkoo and Chatanga - are known to circulate in Scandinavian countries, and parts of Russia. Both are members of the California serogroup in the family Bunyaviridae, and are similar to the mosquito-borne La Crosse Virus found in the United States.

While West Nile virus is the most common cause of neuroinvasive
arboviral disease in the United States, the La Crosse
virus (LACV) is the most common cause among children, producing between 80-100 cases of La Crosse encephalitis each year (cite CDC).

As with both WNV and LACV, most infections are mild or subclinical, and only a small percentage produce significant illness. And like LACV, both Inkoo and Chatanga appear to cause their most severe symptoms in children.

With vector-borne viruses like Dengue, Chikungunya, and Zika on the rise, the following EID journal research article is a good reminder of how much we have yet to learn about mosquito transmitted viruses around the world.

Volume 22, Number 5—May 2016

Research

Abstract

Inkoo virus (INKV) and Chatanga virus (CHATV), which are
circulating in Finland, are mosquitoborne California serogroup
orthobunyaviruses that have a high seroprevalence among humans.
Worldwide, INKV infection has been poorly described, and CHATV infection
has been unknown.

Using serum samples collected in Finland from 7,961
patients suspected of having viral neurologic disease or Puumala virus
infection during the summers of 2001–2013, we analyzed the samples to
detect California serogroup infections. IgM seropositivity revealed 17
acute infections, and cross-neutralization tests confirmed presence of
INKV or CHATV infections.

All children (less than 16
years of age) with INKV infection were hospitalized; adults were
outpatients with mild disease, except for 1 who was hospitalized with
CHATV infection. Symptoms included fever, influenza-like illness, nausea
or vomiting, disorientation, nuchal rigidity, headache, drowsiness, and
seizures. Although many INKV and CHATV infections appear to be
subclinical, these viruses can cause more severe disease, especially in
children.

(SNIP)

In conclusion, we describe INKV and CHATV
infections in humans and the clinical characteristics of acute disease.
Symptoms of acute INKV and CHATV infections in patients in our study
resembled symptoms of other California serogroup virus infections:
influenza-like illness, with fever being most prominent. Most acute
cases appeared to be subclinical, and a small minority of patients
required hospitalization.

Compared with adults, children were at higher
risk for contracting more severe disease and were more often
hospitalized because of INKV infection. In adults, CHATV infection
appeared to be more severe than INKV infection. Further studies are
required to explore in detail the clinical picture, prognosis,
incubation period, and antibody kinetics of these infections. Viral
isolates or RT-PCR–positive samples from patients are needed to acquire
data related to INKV and CHATV strains causing the clinical cases.

Niina Putkuri is a PhD student who works at the Faculty of Medicine,
University of Helsinki, where she is finalizing her thesis. Her research
interests include molecular epidemiology and disease associations of
California serogroup viruses in Finland.